Issue #2847529: check stock availability in add-to-cart form and alter button

[ransomweaver]

This PR only works if commerce is patched with drupalcommerce/commerce#593

This hook_form_alter in commerce_stock_local.module addresses several problems:

1. the base AddToCartForm does not check availability, therefore always allows clicking "Add to Cart" even if not available. PR will check availability and disable button, changing button text to "Unavailable". This will work with whatever stock checker is in use (e.g. commerce_stock_backorderable which overrides the default checker).

2. hook_form_alter AddToCart form object only gives the default purchaseable entity when loading the form via ajax or using query params (product/1?v=2), but if the form uses attributes to select the variation, there is a "selected_variation" storage key that we can use to load the correct variation.

[BBGuy]

Hi @ransomweaver started looking into this and looks to me like we also need to update StockAvailabilityChecker.check as it currently only returns a Boolean or is this in another PR?
Just finishing for the week will continue next week.

[ransomweaver]

@BBGuy You are right. Because I use my commerce_stock_backorderable module that follows PR 593 with its own checker returning AvailabilityResponse, this PR doesn't have the change to StockAvailabilityChecker. It is in PR #12, though that also has an old inferior version of this hook_form_alter code. I suggest you edit PR #12 to remove the change to commerce_stock_local and just take the change to the checker. Also I see I had made a redundant PR #17 that you can close.

[BBGuy]

we should let the stock service determine the text for "Unavailable" but that can go after.

[BBGuy]

Happy for this to go in after drupalcommerce/commerce#593 great work :)

[BBGuy]

I closed the two old PR's and made a new one #38

[GarethSmall]

I modified this a bit so it doesn't require the patch you're speaking about.

function commerce_stock_local_form_alter(&$form, FormState $form_state, $form_id) {
  if (strpos($form_id, 'commerce_order_item_add_to_cart_form') === 0) {
    /** @var \Drupal\commerce_cart\Form\AddToCartForm $form_object */
    $form_object = $form_state->getBuildInfo()['callback_object'];
    
    $storage = $form_state->getStorage();

    $variation = isset($storage['selected_variation']) ? ProductVariation::load($storage['selected_variation'])
      : $form_object->getEntity()->getPurchasedEntity();
    
    if (empty($variation)) return;
    
    $stockServiceManager = \Drupal::service('commerce_stock.service_manager');
    $stock = $stockServiceManager->getStockLevel($variation);
    
    if ($stock <= 0) {
      $form['actions']['submit']['#value'] = t('Out of stock');
      $form['actions']['submit']['#attributes'] = [
        'disabled' => 'disabled',
      ];
    }
  }
}

[steveoriol]

If you use quantity input you can modif as follwing for add the max option:

function commerce_stock_local_form_alter(&$form, FormState $form_state, $form_id) {
  if (strpos($form_id, 'commerce_order_item_add_to_cart_form') === 0) {
    /** @var \Drupal\commerce_cart\Form\AddToCartForm $form_object */
    $form_object = $form_state->getBuildInfo()['callback_object'];
    
    $storage = $form_state->getStorage();

    $variation = isset($storage['selected_variation']) ? ProductVariation::load($storage['selected_variation'])
      : $form_object->getEntity()->getPurchasedEntity();
    
    if (empty($variation)) return;
    
    $stockServiceManager = \Drupal::service('commerce_stock.service_manager');
    $stock = $stockServiceManager->getStockLevel($variation);
    
    if ($stock <= 0) {
      $form['actions']['submit']['#value'] = t('Out of stock');
      $form['actions']['submit']['#attributes'] = [
        'disabled' => 'disabled',
      ];
      $form['quantity']['widget'][0]['value']['#default_value'] = 0;
      $form['quantity']['widget'][0]['value']['#min'] = 0;
      $form['quantity']['widget'][0]['value']['#max'] = 0;
    }
    else {
      $form['quantity']['widget'][0]['value']['#max'] = $stock;
    }
  }
}